1. Field of the Invention
The present invention relates in general to reducing the formation of gases within heat pipes and in particular to a new and useful method for providing a passive oxide layer on the inner surface of heat pipes for decreasing hydrogen generation rates.
2. Description of the Related Art
The use of heat pipes or heat tubes is common in the power generation and chemical process industries. The use of heat pipes has proved to be very efficient at transferring heat between fluids while keeping the fluids from mixing together. Due to the continued use of the heat pipes in the heat transfer processes, corrosion on the interior surfaces of the heat pipes occur, resulting in the formation of incondensible gases such as hydrogen. Because the gases are incondensible, they tend to build up within the heat pipe and reduce the heat pipe's ability to transfer heat thereby decreasing the efficiency and performance.
It has been found that by providing an oxide layer on the interior surface of the heat pipes, the generation rates of the incondensible gases, such as hydrogen, decrease. The hydrogen production is directly related to the formation of a passive oxide layer such as magnetite (Fe.sub.3 O.sub.4) which is formed when carbon steel is exposed to high temperature deaerated water. The reaction responsible for hydrogen generation in water-carbon steel heat pipes is summarized by the equation: EQU 3Fe+4H.sub.2 O.fwdarw.Fe.sub.3 O.sub.4 +4H.sub.2
Because incondensible hydrogen gas generation rates decrease as a passive layer is developed on the interior surface of a heat pipe, a "burn-in" method is used for treating and conditioning fresh carbon steel/water heat pipes. The "burn-in" process is usually conducted using high pressure water through the heat pipes at around 419.degree. F. to 572.degree. F. This "burn-in" process is very time consuming and can take as long as 160 hours.
Other treatments such as steam, gun blueing, and hydrogen peroxide have been used to form a passive oxide layer on the interior surface of the heat pipes. Steam oxidation typically is applied at 890.degree. F. to 1060.degree. F. and requires a high pressure steam source. Gun blueing involves caustic chemicals and hydrogen peroxide is not effective at creating a passive surface oxide layer on carbon steel.
Although several passivation processes exist for providing a passive oxide layer on the interior surface of carbon steel heat pipes, there is no known process which is both economical and can be performed in a short amount of time.